I'm borderline on the obesity issue, since obesity has been shown to be genetic.
Therefore I would set it up thusly.
I would provide gyms with tax breaks for admitting those whose obesity is a danger to their health. Along with the tax breaks would come a few minor obligations. Excercise cards would be given out to the obese, and they would work like punch cards inside a gym, with the punch card machines being given to the gyms who apply for the tax breaks. So, if the obese individual can prove he is trying, he will recieve medical care. A reasonable number of hours that constitutes a reasonable effort will be decided and agreed upon by experts, and if people tried to cheat, there would be cameras in the gyms that applied for tax breaks. Those that do not try to improve will not recieve medical care for obesity-related ailments.